Electromechanical Characterization of Advanced Internal-Tin Nb₃Sn Strands for the DTT Magnet System

This paper presents a practical parameterization of the critical surface of the 0.82-mm diameter Nb3Sn strands used for the Toroidal Field coils of the Italian Divertor Tokamak Test Facility. The critical current has been measured by means of a Walters Spring device as a function of uniaxial applied strain (+/- 0.5% intrinsic strain) at different field (up to 14 T) and in the temperature range comprised between 4.5 K and 10 K. The experimental results have been analyzed in the framework of the ITER-2008 parameterization and the Extrapolative Scaling Expression, by using a multi-step approach for the data fitting. The accuracy of the scaling laws provides an accurate parameterization of the critical surface in terms of field, temperature and strain, to be used for the characterization and production follow-up of the DTT qualification samples and coils.